This project addresses two issues of relevance to behavioral medicine: 1) study of changes in health-related behavior by myocardial infarction patients; and 2) study of the phenomenon of relapse to substance abuse (cigarette smoking). Chronic cigarette smokers who are admitted to the Coronary Care Unit following acute myocardial infarction will be studied in order to: 1) describe the prevalence, time-course and process of post-MI smoking relapse; 2) identify correlates and predictors of post-MI smoking relapse and smoking cessation; and 3) evaluate the efficacy of an in-hospital intervention for reducing the prevalence of post-MI smoking relapse. An A-B-A experimental design will e used, in which patients during years 1 and 3 of the project will receive standard treatment, while patients during year 2 will receive an intensive non-smoking intervention throughout their hospitalization. The non-smoking intervention will be limited to techniques which can reasonably be replicated in other medical settings, and will involve strong, directive non-smoling instructions by the physician, daily feedback of expired breath CO level to the patient, and involvement of family and visitors in non-smoking efforts. Follow-up of up to two years duration will assess the stability of smoking status over time and will assess post-MI morbidity and mortaility. Smoking status will be assessed throughout the study using both self-report and the objective measure of expired breath CO level. A variety of situational, historical, psychological, and medical variables will be assessed and examined as possible correlates or predicators of smoking relapse or smoking cessation.